DanielLC wrote: If we didn't care about them, we'd just leave them alone. The only reason to kill them is that we consider that a better alternative.
Our reasons for capturing cats and dogs are often just as much, if not more, for human purposes, e.g. that we do not want them to make a mess out of our cities, that we want to avoid stray animals to spread diseases and bite people etc.
A better alternative for what? The reason why healthy animals are put down is that we do not have space and resources for them, and this proves the very point that we do not care enough about them. Killing healthy individuals out of a lack of resources is simply not what we do to individuals whom we truly care about (think: humans). And yeah, it is not that we do not care about cats and dogs at all -- at least they do not have the same status as chickens and pigs whom we find it perfectly fine to fry and eat. Yet it is still a pale form of care we show, which is practically inevitable as long as they are property and have commodity status.
DanielLC wrote: Raising them would be better still, but that's not an option for wild animals.
Mass euthanasia or sterilizing is not yet an option either. In the future it could be, and if/when we attain such technological sophistication, we will likely to be able to steward the life of at least many wild animals. We could likely do this now already, at least resource-wise, yet we obviously do not have the will and mindset it takes, because we think about wild animals in terms of conservation and populations rather than welfare, and because it makes little sense, economically and ethically, to take care of small groups of wild animals while we impose suffering upon billions of them and find it perfectly acceptable to kill them for frivolous reasons.
DanielLC wrote: I don't see how antinatalism could be the best option. Either wild animals' lives are worth living, in which case we should let them reproduce, or they are not, in which case we should end them as soon as possible.
It is hardly that simple. Excuse me for making a bizarre thought experiment, but say we have a population of humans on an isolated island, and say this population is able to reproduce, but their lives are clearly not worth living in the aggregate. Important to note is that it is not that their lives are not worth living most days of their lives, but rather that they have very painful final years and deaths that make them suffer horribly when they die, and which make their lives big minus signs on the whole (one could argue that this applies to most humans in general, but that is not the issue here). To make the thought experiment even more bizarre and similar to the horrors of nature, let's say they tend to die by getting eaten alive by the other humans, and since these humans all have have a genetic defect, this is how they will inevitably act if we do not intervene, and we cannot convince them to use contraception or otherwise not have children (I believe this is fairly analogous to the situation of many, if not most, animal lives in nature -- not cannibalism, although it's not uncommon, but that wild animals eat each other, and live terrible lives in the aggregate, even if most of their lifetime is more than bearable).
Now, the question is: How do we best deal with this situation? Do we simply mass euthanize them? It does not seem like such an obvious solution to me, and ditto for the animals in nature. Forced sterilization combined with some intervention -- such as providing them adequate, cruelty-free food -- is much better in my view.